2,5-Dimercapto-1,3,4-thiadiazole is a known compound and has been reported in British Pat. No. 974,915 as a curing agent for certain unsaturated, halogen-containing polymers (i.e., chlorobutyl rubber and polychloroprene elastomers). However, the compositions disclosed in British Pat. No. 974,915 will not cross-link saturated, halogen-containing polymers.